Field of the Invention
The present invention relates to a device to increase the dynamic ratio of an amplifier circuit, especially that of an on-board MLS receiver.
The MLS (microwave landing system) uses a signal which has the format of a pulse-time multiplexed signal. This multiplexed signal may consist, in particular, of data relating to the rear azimuth, elevation and flattening-out angles as well as auxiliary data. These different functions are transmitted by different antenna, and this fact can give rise to sharp variations in level between one function and another.
In order that the on-board receiver which has to receive the MLS signal may function properly in the face of these variations in the level of the signal, it has been sought to use a linear amplifier fitted with an automatic gain control system, but this solution has proved to be difficult to use because the different functions of the MLS are transmitted at a pseudo-random rate. It has also been sought to use a logarithmic amplifier, but the dynamic ratio of such an amplifier is far too limited for this application. This fact entails the risk that the amplifier might be saturated in the presence of high-level signals, a phenomenon that does not affect the preamble, which is phase-modulated, but affects the angle signals which are transmitted by amplitude modulation.
The object of the present invention is a device by which it is possible, in a simple and economical way, to increase the dynamic ratio of a receiver, especially an on-board receiver for an MLS system.